Alarm went off, but no sensor was triggered.

Last night our alarm randomly sounded, but it was not triggered by any sensor. When I look at the history, it shows we armed it in the evening and the next activity is early in the morning when we had to disarm it for sounding. Do we need to have someone come out and look at the system? Also, it wasn't the normal alarm sound when a door or something triggers it; it was quieter and the siren seemed more spaced out.